1. Field of the Invention
The present invention relates to an electrical bushing that is particularly useful for facilitating the passage of a plurality of signal leads or conductors from thermocouples or the like through a pressure barrier or wall defining the pressure chamber which surrounds the furnace space in a pressure furnace of the kind which is used for treatment of workpieces at high temperatures and simultaneously at high pressures. The furnace may, for example, be of the type which is described in greater detail in U.S. Pat. No. 3,790,339.
2. Description Of The Prior Art
Bushings of the type to which the present invention relates generally comprise an elongated bushing casing which is inserted into a bored recess or opening extending through a pressure barrier such as the end closure for a pressure vessel. Typically the casing is provided with a shoulder formed between two adjacent portions or lengths having different diameters. The shoulder on the casing abuts against a similarly formed shoulder in the bored recess to thereby establish and fix the positioning of the bushing in the opening and relative to the pressure barrier. The bushing unit is generally intended for accommodation of a large number of conductors.
In known bushings, the conductors are cast into long holes in, for example, polystyrene core elements which are then polymerized further to obtain a sufficient strength to resist the applied pressure differential. In other known bushings the conductors are cast into a joint made of a thermosetting resin, such as, for example, an epoxy resin, in a gap provided in the joint between a conical wall in a hole and a conical plug. In these known bushings it has been practically impossible to remove the conductors for insertion of new ones after the bushing is once installed. Thus, from the point of view of maintenance and service, these prior bushings are less suited for commercial operation on an industrial scale where, of course, the easy performance of service and maintenance operations is of vital importance.